1. Field of the Invention
This invention relates to an alert or alarm system for determining the location of a ground based beacon or transmitter relative to a central surface location at a short time after activation of the beacon by means of an orbiting antenna which has scanning capabilities.
In particular, the purpose of this system is to provide a means of determining the position of ground based beacons relative to a central location within seconds after activation of the beacon. Thus, rapid location of vehicles in distress such as ships at sea, auto wrecks, airplane crashes, or any other basic alarm function can be quickly located.
2. Description of the Prior Art
Prior proposals for this type of alarm have involved complex and large electronic systems fixed to ground locations at close spacings. Over a large area, this is not practical and it fails to cover situations over a body of water. Prior art patents include U.S. Pat. No. 3,048,839 which discloses the use of a surveyor transceiver unit which provides bearing and range data relative to locator stations. In U.S. Pat. No. 3,678,387, a satellite two-way communications system used a phase array antenna. In U.S. Pat. No. 3,483,561, a direction finding system is disclosed which uses plural circularly arranged antenna elements and a phase shifter. A doppler system is disclosed in U.S. Pat. No. 3,254,341 for calculating the coordinates of a point on the earth's surface wherein a satellite's radiated signals are received by a vehicle on the earth's surface from which the vehicles position may be computed. In U.S. Pat. No. 3,541,553, a satellite in a satellite communications system is placed in synchronous orbit and transmits an irregularly shaped beam by means of a plurality of antennas.
None of these systems for determining locations has the simplicity or accuracy provided by the present invention. In the present invention, a ground based beacon is located by a geosynchronous satellite within two kilometers on the surface of the earth with the total search area being about the size of the continental United States. In the present system, there is a ninety percent probability of detection within ten seconds after turn-on of the ground beacon.